Mosaic printing head

ABSTRACT

A printing head for a mosaic printer includes a ring-shaped structure which supports a mounting bracket, and a number of guiding tubes for the printing needles are mounted on the bracket. Each of the guiding tubes has a plurality of openings and is surrounted by a porous oil impregnated sleeve for lubricating the needles. An electromagnetic actuator for each needle is mounted on the ring and includes a movable armature which engages an end of the corresponding needle when the actuator is energized. The core of the actuator is adjustably mounted on the ring, and an adjustment screw adjust the width at rest of the air gap and the stroke of the needle. A hinged elastic system connects the armature to the yoke of the actuator and includes a curved rider to provide rolling contact with the yoke.

United States Patent Cattaneo 11] 3,889,793 June 17, 1975 MOSAIC PRINTING HEAD [75] Inventor:

[73] Assignee: Honeywell Information Systems Italia, Caluso, Italy [22] Filed: June 14, 1973 21 Appl. No.: 370,136

Sergio Cattaneo, Voghera, Italy [30] Foreign Application Priority Data June 15, 1972 Italy 25698/72 [52] US. Cl. 197/1 R; 101/9305 [51] Int. Cl B41j 3/05 [58] Field of Search 197/1 R; 101/93 C; 335/274-276 [56] References Cited UNITED STATES PATENTS 2,728,289 12/1955 Johnson et al. 197/1 R X 2,928,338 3/l960 Wockenfuss l97/l R X 3,302,562 2/1967 Nelson 197/1 R X 3,333,667 8/1967 Nordin l97/l R 3,690,431 9/l972 Howard l97/l R 3,698,528 10/1972 DeGraff 197/] R 3,782,520 l/I974 Howard 197/1 R FOREIGN PATENTS OR APPLICATIONS 1,577,409 8/!969 France l97/l R OTHER PUBLICATIONS Meir, Mechanical X-Y Aiming of Ink Jet Printer Nozzles, IBM Tech. Discl. BulL, Vol. 15, No. 5, 1972.

Primary Examiner-Edgar S. Burr Assistant ExaminerR. T. Rader Attorney, Agent, or Firm-Fred Jacob [5 7] ABSTRACT A printing head for a mosaic printer includes a ringshaped structure which supports a mounting bracket, and a number of guiding tubes for the printing needles are mounted on the bracket. Each of the guiding tubes has a plurality of openings and is surrounted by a porous oil impregnated sleeve for lubricating the needles. An electromagnetic actuator for each needle is mounted on the ring and includes a movable armature which engages an end of the corresponding needle when the actuator is energized. The core of the actuator is adjustably mounted on the ring, and an adjustment screw adjust the width at rest of the air gap and the stroke of the needle. A hinged elastic system connects the armature to the yoke of the actuator and includes a curved rider to provide rolling contact with the yoke.

7 Claims, 3 Drawing Figures MOSAIC PRINTINGIHEAD BACKGROUND OF THE INVENTION The present invention relates to impact printers used in data processing systems in which the printing of each character is obtained by means of a set of points.

In such printing devices, the impression by points of a single character on paper is obtained by projecting towards a platen located on the back of the printing media the ends of a subset of metallic needles chosen among a set according to the form of the characters to be printed.

The impression may be accomplished at the same instant of time or in subsequent times by horizontally scanning the character form. I

In the first case, the number of needles generally used is thirty-five arranged to form a matrix of5 X 7 possible points of impression.

In the second case, there is provided, in general, a vertical comb of seven needles accomplishing a horizontal scanning of the character.

In both cases, the impression needles and the respective actuation electromagnets are assembled in general on a carriage movable along the printing line to be in condition to carry on the sequential or serial impression of several characters. They form a movable printing head on the carriage. The size of the electromagnets of the guiding systems of the needles and the problems of inertia, of the necessary power supply, and of dissipation cause the solution using a seven needle comb to be usually preferred. Even so, the size and inertia problems of the movable carriage are not entirely solved and serious problems arise in guiding and lubricating the needles and in adjusting the stroke of the same; the last is most important, as the actuating frequency of the needles is very high, and the maximum frequency obtainable is strongly influenced and limited by said stroke.

SUMMARY OF THE INVENTION The device according to the invention avoids these inconveniences and improves the condition of operation of the impression head.

According to a first characteristic of the invention, the guiding of the needles is assured practically on all their length, by guides, having a suitable degree of rigidity, within which the needles may slide, said guides being provided with proper lubricating means ensuring a suitable lubrication along their whole length.

According to a second characteristic of the invention, the actuating electromagnets associated with the needles are not rigidly fastened to the printing carriage, but they are mounted through the interposition of micrometric adjusting devices which allow individual adjustment both of the width at rest of the air gaps of said electromagnetic actuators and the strokes of the needles.

The adjusting devices are in addition easily accessible; therefore the adjustments are particularly easy.

According to another characteristic of the invention, the movable armature of each electromagnet is connected to the fixed part by means of a hinged elastic system which insures a minimum contact surface, and an automatic recovery of the clearances'and, at the same time, does not introduce elastic reactions hindering the rotation of the movable armature.

By such means it is possible to obtain a printing assembly having a reduced size, high reliability, and highly repetitive performances, particularly advantageous for those applications in which a high printing speed is required.

SHORT DESCRIPTION OF THE DRAWINGS The characteristic features and advantages of the invention will appear clearly from the following description having exemplifying and not limiting purposes and by the attached drawings in which:

FIG. 1 is a sectional side view of a preferred embodiment of a printing head according to the invention:

FIG. 1a is a perspective view of a detail of the guiding elements for the impression needles used in the printing head according to the invention; and

FIG. 2 is an exploded perspective view of the elements forming an electromagnetic actuator used in the printing head according to the invention. A

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 represents a sectional side view of a printing head according to the invention.

The head consists of a rigid support mounted on a carriage sliding on guides consisting essentially of ring I (seen in section) and of bracket 2 fixed thereto, for example by means of screws such as screw 3. The ring 1 has essentially the function of supporting a certain number, for example seven, or nine, of electromagnetic actuators while bracket 2 has essentially the function of supporting an equal number of printing needles.

The bracket 2 is provided at one end with a flange 4 having some openings 5 radially located with respect to a center, and at the opposite end witha guiding member 6, with holes or grooves, in which some jewels, not shown, are mounted to serve as guides for the ends of the printing needles, as the one indicated by 7.

Near the guiding member 6, and between member 6 and the flange 4, there is a second flange 8 having several openings 40. Each printing needle is guided from the flange 4 to the flange 8 by a thin guiding tube 9. Each guiding tube 9 is inserted freely in a corresponding opening 5 of flange 4 and at the opposite end is inserted in a corresponding opening 40 of flange 8 and fixed to it through soldering or cementing.

The guiding tubes have at intervals some openings 10 (better shown in FIG. la) obtained by milling. The tubes are covered, for their whole length, except the part nearest the wing 8, with sleeves 11 of porousmaterial with negligible mechanical rigidity, for example felt or braiding. The sleeves are dipped in lubricating oil, and they insure through the openings 10 a practically uniform lubrication within the guiding tubes, supplying the lubricating oil when needed and absorbing it when in excess. The thickness of the tubes and the number of openings are chosen so to obtain a suitable but not excessive rigidity of the tubes themselves. In fact, the printing needles behave during the operation as tiploaded rods whose rigidity results from the sum of their intrinsic rigidity and that of the guiding tubes.

As it is known there is a critical load, which is a function of the constraint conditions and of the rigidity of the rod, beyond which the rod gives up and bends. Choosing a suitable rigidity for the guiding system, it is possible for it to act so that the pressure exerted by the printing needles does not exceed a pre-fixed value corresponding to the critical load; and it is therefore .possible to obtain an exceptionally constant exerted printing force independent from the force exerted by the actuators on the needles, which may be chosen at an average design value somewhat exceeding the critical load, so that possible differences due to variations in the energization conditions, to differences in the magnetic behaviour of the materials, or the like are automatically corrected.

At the end opposite to the printing side, the needles have a small head 12 designed to cooperate with an actuating arm 13 of the movable armature 14 of the electromagnetic actuators. Every needle is also supplied with a compression spring 15, with suitable elastic constant, acting between wing 4 and the head 12 of the needle and tending to push the needle itself and the movable armature 14 toward a rest position.

The electromagnetic actuators, of the so called flat type, consist of a central cylindrical core 16, of ferromagnetic material on which an electric winding 17 is assembled, of a U-shaped yoke 18, also of ferromagneitc material, and of a movable armature 14.

With reference both to FIG. 1 and to FIG. 2, it is possible to observe that the yoke 18 has a threaded hole 19 which is screwed on the end portion of the core 16. The core 16 continues with a cylindrical projection 20 which enters a corresponding axially directed opening of the ring 1. The projection 20 is provided with an axial threaded hole in which the adjustment screw 21 is screwed. The screw 21 has, for example, in the screw head portion thereof, a groove 22 in which a retaining member 23 fixed to the ring 1 is inserted. In FIG. 2, this retaining member is represented partially and consists of a ring having suitable notches 24 which fit the grooves of the adjustment screws. The retaining member 23 is, for example, fixed to the circular body 1 through screws, such as the one indicated at 25.

It is clear that by acting on screw 21, thus engaged by the retaining member, it is possible to cause precise axial displacements of the electromagnetic actuator, with respect to the support. A clamping screw 26 inserted in a radial threaded hole made on the ring 1 in correspondence to each projection 20, allows each electromagnetic actuator to be locked rigidly in position.

The yoke 18 of the actuators has one arm considerably longer than the other arm 36 and in this one arm there is an opening 27 in which an extension 29 of the movable armature is housed. A steel rider 28 having an opening 30 is inserted on the extension 29 and leans against the end of the armature.

A U-shaped spring 31, drilled and inserted on extension 29 and locked thereto by means of a clamp 32 which is inserted in two recesses 33 of the extension 29, exerts a pulling force on the armature in such a way that the end of the armature and the corresponding rider are strongly pushed against the side of the one arm of the yoke 18 near the opening 27. In this way the armature is tied to the yoke, but it is free to roll on the yoke surface, presenting a limited surface of rolling contact, and therefore a minimal friction; and, on the other hand, no substantial elastic reactions opposed to the rotation of the armature are introduced.

A screw adjusting the stroke of the armature and an anti-sticking plate complete the actuator. The antisticking plate 34 is made of non-magnetic material and is cemented to the arm 36 of the yoke l8.

The armature is drilled to provide a passage for the adjustment screw 37 which is screwed into a threaded hole of the core 16. The screw 37 has a head considerably larger than the hole drilled in the armature, so that it limits effectively the maximum width of the air gap between the core and the armature and therefore the stroke of the armature itself.

FIG. 1 shows that the spring 15 through the head 12 of the needle exerts a pressure on the armature 14 and tends to make it lean in rest position against the head of the adjustment screw 37.

Although FIGS. 1 and 2 show only one electromagnetic actuator and a needle with related guiding system, it is clear that the several (for example seven or nine) electromagnetic actuators are arranged radially on the ring 1, and a corresponding plurality of needles is assembled on bracket 2, the needles being guided by the above described tubes.

The described structure, which is mechanically simple and strong, has the advantage of allowing individual adjustment of the stroke of the electromagnetic actuators and individual positioning of each actuator with respect to the corresponding printing needle.

The adjustment devices are all set externally with respect to the structure of the printing head, for an easy adjustment of the different parts; and therefore uniform performances of the different impression needles and excellent print quality may be obtained.

In addition, it must be observed that the system of tying the movable armature to the yoke provides automatically for the compensation of the clearances resulting from possible wear at the contact point and also provides therefore highly repetitive behaviour of the actuator for very long service periods without requiring interventions for adjustments or replacement of the worn parts.

The invention claimed is:

1. A printing head for a mosaic printer wherein a plurality of movable needles are projected against a platen, said printing head comprising a ring-shaped structural supporting member, a bracket firmly connected to said ring-shaped member, said ring shaped member having a plurality of axial openings distributed circumferentially with respect to said bracket; a plurality of guiding members for said movable needles mounted on said bracket; a plurality of flat electromagnets, each electromagnet comprising a rotatable armature, a central core, a U-shaped yoke and a cylindrical projection coaxial to said central core and engaged in a corresponding one of said axial openings of said ringshaped member; each cylindrical portion and its respective axial opening defining individual means for mounting a respective one of said electromagnets in axially adjusted position; individual locking means for locking each said electromagnet in the adjusted position; individual means for adjusting the air gap between said armature in rest position and said central core; and means for securing said armature to said yoke in a manner allowing a limited rotation of said armature substantially free from restoring torques.

2. The printing head of claim 1, together with axial adjustment means for said electromagnets includes a first adjustment screw coaxial to said projection and engaged in a threaded hole provided on said projection, locking means fixed to said ring-shaped member for preventing the axial movement of said adjustment screw, said locking means including a locking screw engaged in a radial threaded hole in said ring-shaped member and acting on said projection.

3. The printing head of claim 1, in which said air-gap adjusting means includes an adjustment screw engaged in a threaded hole coaxial to said central core, said movable armature being provided with an opening for allowing said screw to freely pass through said armature.

4. The printing head of claim 1, wherein said means for securing said armature to said yoke includes an extension of said armature, an opening in said yoke for receiving said extension, an elastic means acting on said extension and said yoke for maintaining said extension within said opening.

5. The printing head of claim 4, wherein said means for securing said armature to said yoke includes a rider mounted on said armature and cooperating with said yoke to form a turning member having a limited contact surface.

6. The printing head of claim 1 wherein said ringshaped support has a central opening, and said bracket extends through said central opening to opposite sides of said ring-shaped support.

7. The printing head of claim 1 wherein each needle includes a head in abutting engagement only with its respective armature. 

1. A printing head for a mosaic printer wherein a plurality of movable needles are projected against a platen, said printing head comprising a ring-shaped structural supporting member, a bracket firmly connected to said ring-shaped member, said ring shaped member having a plurality of axial openings distributed circumferentially with respect to said bracket; a plurality of guiding members for said movable needles mounted on said bracket; a plurality of flat electromagnets, each electromagnet comprising a rotatable armature, a central core, a U-shaped yoke and a cylindrical projection coaxial to said central core and engaged in a corresponding one of said axial openings of said ring-shaped member; each cylindrical portion and its respective axial opening defining individual means for mounting a respective one of said electromagnets in axially adjusted position; individual locking means for locking each said electromagnet in the adjusted position; individual means for adjusting the air gap between said armature in rest position and said central core; and means for securing said armature to said yoke in a manner allowing a limited rotation of said armature substantially free from restoring torques.
 2. The printing head of claim 1, together with axial adjustment means for said electromagnets includes a first adjustment screw coaxial to said projection and engaged in a threaded hole provided on said projection, locking means fixed to said ring-shaped member for preventing the axial movement of said adjustment screw, said locking means including a locking screw engaged in a radial threaded hole in said ring-shaped member and acting on said projection.
 3. The printing head of claim 1, in which said air-gap adjusting means includes an adjustment screw engaged in a threaded hole coaxial to said central core, said movable armature being provided with an opening for allowing said screw to freely pass through said armature.
 4. The printing head of claim 1, wherein said means for securing said armature to said yoke includes an extension of said armature, an opening in said yoke for receiving said extension, an elastic means acting on said extension and said yoke for maintaining said extension within said opening.
 5. The printing head of claim 4, wherein said means for securing said armature to said yoke includes a rider mounted on said armature and cooperating with said yoke to form a turning member having a limited contact surface.
 6. The printing head of claim 1 wherein said rinG-shaped support has a central opening, and said bracket extends through said central opening to opposite sides of said ring-shaped support.
 7. The printing head of claim 1 wherein each needle includes a head in abutting engagement only with its respective armature. 